Hard disk drive suspension with integral flexible circuit

ABSTRACT

A disk drive suspension assembly including an elongated polymeric base member having a plurality of traces formed directly on a first surface thereof and a reference voltage layer formed on a second surface thereof. A support member is formed directly on at least a portion of the reference voltage layer. The plurality of traces overlay at least a portion of the reference voltage layer. The reference voltage layer is formed from a first electrically conductive material and the support member is formed from a second electrically conductive material. The first electrically conductive material providing substantially greater electrical conductivity and substantially less tensile strength than the second electrically conductive material. The support member includes a head gimbal portion having a first thickness and a load beam portion having a second thickness. The second thickness is substantially greater than the first thickness.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Ser. No. 09/567,783,filed on May 9, 2000 U.S. Pat. No. 6,480,359.

FIELD OF THE INVENTION

The invention disclosed herein relates generally to hard disk drivesuspensions. More specifically, the invention relates to hard disk drivesuspension assemblies and circuit assemblies with an integral flexiblecircuit and integral support member.

BACKGROUND OF THE INVENTION

Suspension assemblies in hard disk drives include a head gimbal assembly(HGA). The HGA includes a gimbal assembly, a head assembly, and aninterconnect assembly. The head assembly includes a highly sensitiveread/write transducer, commonly referred to as a head, attached to anair bearing slider. The head assembly also includes electrical terminalsconfigured for interconnection to the interconnect assembly forreceiving and relaying data signals. The head assembly facilitatesreading and writing of information on a surface of a rotating magneticdisk. The interconnect assembly includes a plurality of transmissionelements, such as wires or traces, for transmitting data to and from thehead assembly. The suspension assembly positions the head assembly at agenerally constant distance away from the moving surface of the rotatingdisk. The suspension assembly permits the head assembly to “fly” at aheight above the surface of the disk, including surface irregularities.

Most conventional suspension assemblies, also referred to herein as asupport member, include a load beam and a gimbal portion. The load beamis a resilient spring plate designed to provide lateral stiffness. Theload beam is calibrated to apply a force on the head assembly thatcounteracts a lift force on the head that is provided by the air streamgenerated by the rotating disk. Accordingly, the head assembly fliesabove the surface of the disk at a height established by the equilibriumof the load beam force and the lift force.

The gimbal portion is positioned adjacent to an end of the load beam andhas the head assembly attached thereto. The gimbal portion permits rolland pitch deflections of the head assembly in response to flying oversurface imperfections and warping of the rotating disk. By permittingthese deflections, the gimbal portion aids in maintaining the properorientation and distance of the head assembly relative to the rotatingdisk, even when the load beam exhibits a slight amount of flexing andtwisting.

The suspension assembly can be attached at its proximal end to a rigidarm or directly to a linear or rotary motion actuator. The actuatorrapidly moves and then abruptly stops the HGA over any position on aradius of the disk. The radial HGA movement and the rotation of the diskallow the head to quickly reach every location above the disk. However,the rapid stop and go movement causes very high stresses on the HGA.

An ideal HGA comprises components low in mass. Excessive inertialmomentum caused by excessive mass can cause overshoot errors. Overshooterrors occur when momentum carries the whole HGA past the intendedstopping point during positioning movement. Low-in-mass HGA's are easierto move, resulting in power savings in multiple platter disk drives.Furthermore, lighter weight HGA's permit the head to be flown closer tothe surface of the disk. The closer the head assembly can fly to thesurface of the disk, the more densely information can be stored on thedisk. Accordingly, a lightweight HGA is desirable in high performancedisk drives.

It is known that the strength of a magnetic field in a disk drive variesproportionally to the square of the fly height of the head.Manufacturers of disk drives strive to reach flying clearances less than100 nanometers, which is 0.1 micrometers. For comparison, a human hairis about 100 micrometers thick. However, the head assembly must nottouch the disk, since the impact with the spinning disk, which rotatesat about 10,000 rpm or faster, can damage the head and the surface ofthe disk.

Amplifying and control circuits process, send and receive the datasignals to and from the head assembly. Signal transmission requiresconductors to extend between the head assembly and the related circuitryof the disk drive. Traditional head assemblies use a read-write circuitloop with two conductors, usually copper wires encapsulated in plasticsheeting. Newer types of magnetic read-write heads, commonly referred toas magneto-resistance head assemblies, require four or more independentconductors.

The increasing need for more wires, lower disk stack height and lessstiffness and mass of the suspension assembly has forced themanufacturers to consider different suspension design approaches. In onedesign approach, a suspension assembly has signal traces that are etchedfrom a stainless steel based material and an insulating layer issubsequently formed over the signal traces. The stainless steel basematerial is also etched to form the load beam portion and head gimbalportion of the suspension. A key limitation of this type of constructionis excessive yield rates due to the integrated fabrication process andpoor conductivity of stainless steel. In another design approach, aconventional flex circuit is attached to a separately fabricatedsuspension assembly using an adhesive. A key drawback with this type ofconstruction is the cost associated with the precision required forassembling the flexible circuit to the suspension assembly.

Designers and manufacturers of HGA's face competing and limiting designconsiderations. During operation, the suspension assembly should be freeof unpredictable loads and biases which alter the exact positioning ofthe head assembly. The suspension assembly should respondinstantaneously to variations in the surface topology of a disk.Alterations to the flying height of the head can significantly affectdata density and accuracy and even destroy data stored on the disk ifthe head collides with the surface of the disk.

The rigidity and stiffness of a load beam increase in relation to thecross-sectional thickness by the third power. To respond to air streamchanges and to hold the flying head at the appropriate orientation,suspension assemblies are very thin and flexible, especially around asensitive spring portion of the load beam. Interconnect assemblyconductors have a large effect on the performance of the suspensionassembly. Conductor stiffness alone greatly affects the rigidity of thespring regions and flight performance.

A standard wire conductor attached atop the suspension can more thandouble the stiffness of a load beam and significantly limit the abilityof the load beam to adjust to variations in the surface of the disk,vibrations, and movement. The effect of the conductors on a gimbalregion, the thinnest and most delicate spring in the suspensionassembly, is even more pronounced. Furthermore, conductors placed overspring regions of the load beam and gimbal portion of the suspensionassembly must not plastically deform when the spring regions flex.Plastic deformation prevents the return of the load beam or gimbalportion to its normal position and applies a biased load on thesuspension assembly.

In HGA's that use conventional wire interconnect assemblies, two to fivelengths of wire to the head assembly are manually connected to the head.Fixtures are used to manage the wires while they are being bonded to thehead assembly. The lengths of wire are manually shaped using tweezersand tooling assistance to form a service loop between the head assemblyand the suspension assembly and to position the wire along apredetermined wire path on the suspension assembly. The wires are tackedto the suspension using an adhesive or wire capture features formed intothe suspension.

Special care is taken to avoid pulling the service loop too tight orleaving it too loose. A tight service loop places an unwanted torque onthe head assembly causing errors associated with the fly height. A looseservice loop allows the wire to sag down and scrape the adjacentspinning disk. Both conditions are catastrophic to disk driveperformance.

Throughout the process of handling the head assembly, interconnectassembly and the suspension assembly, there is a risk of damaging thewires or the delicate load beam and gimbal. Load beams or gimbalsaccidentally bent during the manufacturing operations are scrapped.Often the head assembly also cannot be recovered, adding additionalfinancial losses.

Similar to conventional wire interconnect assemblies, flexible circuitinterconnect assemblies may inadvertently impart unbalanced or excessiveforces on the suspension. Many common flexible circuit case substratesare also hydroscopic, resulting in flexural characteristics that aredependent on moisture content and humidity. Because the flexiblecircuits are formed separately from the suspension and subsequentlyattached, precision manufacturing tolerances are difficult and costly tomaintain.

Therefore, what is needed is a circuit assembly for a disk drive headsuspension that provides improved fly height control, that reduces noisein signal transmission to and from the head assembly, and that can becost effectively manufactured.

SUMMARY OF THE INVENTION

Accordingly, in one embodiment of the present invention, a circuitassembly includes a base member and a plurality of traces formeddirectly on a first surface of the base member. The traces extendbetween a first end and a second end of the base member. A referencevoltage member is formed directly on a second surface of the basemember. The plurality of traces is positioned to overlay at least aportion of the reference voltage member. A support member is formeddirectly on at least a portion of the reference voltage member.

The support member is formed from a material exhibiting a tensilestrength substantially greater than the tensile strength exhibited bythe reference voltage member and the traces. A preferred material forthe support member is a nickel alloy such as nickel boron ornickel-phosphorus or any suitable plateable material. A preferredmaterial for the traces is copper, gold, palladium, tin, or any suitableplateable. In a preferred embodiment, the traces and the referencevoltage member are formed of the same material.

The support member is preferably formed directly on the referencevoltage member using an electroless plating process. The electrolessplating process is preferably an autocatalytic electroless platingprocess. The use of an electroless plating process contributes toproviding a support member with uniform thickness and allows the supportmember to be made from a preferred selection of materials.

The support member may be formed to have regions of different thicknessas well as regions that are completely isolated from adjacent regionsthereof. A load beam portion of the support member preferably has athickness substantially greater than a gimbal portion thereof. The loadbeam portion of the support member may include spaced-apart flangeportions having a main portion extending therebetween. The flangeportion of the support member has a thickness substantially greater thanthe main portion of the support member.

Circuit assemblies and suspension assemblies according to the presentinvention exhibit an impedance value of less than about 200 ohms betweenany two traces.

In another embodiment of the present invention, a process for making acircuit assembly includes the steps of forming a plurality of tracesdirectly on a first surface of a base member, wherein the traces extendbetween a first end and a second end of the base member; forming areference voltage layer directly on a second surface of the base member,wherein the plurality of traces overlay at least a portion of thereference voltage layer; and forming a support member directly on atleast a portion of the reference voltage layer.

In a further embodiment of the present invention, a disk drivesuspension assembly includes an elongated polymeric base member having aplurality of traces formed directly on a first surface thereof and areference voltage member formed on a second surface thereof. A supportmember is formed directly on at least a portion of the reference voltagemember. The plurality of traces overlay at least a portion of thereference voltage member. The reference voltage member is formed from afirst electrically conductive material and the support member is formedfrom a second electrically conductive material. The first electricallyconductive material provides substantially greater electricalconductivity and substantially lower tensile strength than the secondelectrically conductive material. The support member includes a headgimbal portion having a first thickness and a load beam portion having asecond thickness. The second thickness is substantially greater than thefirst thickness.

The following terms have the following meanings when used herein:

1. The term “electroless deposition” refers to processes in which alayer of material is deposited onto a non-conductive substrate.

2. The term “electroless plating” refers to processes in whichconductive features on a substrate are plated without being subjected toan externally applied current or voltage.

3. The term “autocatalytic electroless plating” refers to a process ofdepositing a metallic coating by a controlled chemical reduction where areducing agent in the form of a chemical, such as sodium hypophosphite,provides the electrons.

4. The term “head suspension assembly (HGA)” refers to a structureincluding a gimbal assembly, a head assembly, and an interconnectassembly.

5. The term “suspension assembly” refers to a structure including a loadbeam portion and a head gimbal portion.

6. The term “load beam” refers to a portion of the suspension assemblythat provides a flexural-induced loading relative to a longitudinal axisthereof and that exhibits negligible torsional deflection relative tothe longitudinal axis.

7. The term “gimbal portion” refers to a portion of the suspensionassembly that permits pitch and roll movement of the slider.

8. The term “support member” refers to a structural member including theload beam and optionally including a gimbal portion.

9. The terms “slider” and “head” are used interchangeably herein andrefer to a unit for reading and writing information in a magneticformat, optical format or other type of data storage format.

10. The term “reference voltage layer” refers to a layer of electricallyconductive material that is spaced away from an adjacent electricalfeature by a uniform distance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an embodiment of a disk drivesuspension assembly.

FIG. 2 is a perspective view illustrating a head gimbal portion of thedisk drive suspension assembly of FIG. 1.

FIG. 3 is a different perspective view of the head gimbal portion ofFIG. 2.

FIG. 4A is a cross-sectional view taken along the line 4A—4A in FIG. 1.

FIG. 4B is a cross-sectional view taken along the line 4B—4B in FIG. 1.

FIG. 5 is a perspective view illustrating a disk drive circuit assemblyfor use with a conventional disk drive load beam.

FIG. 6 is a cross-sectional view taken along the line 6—6 in FIG. 5.

FIGS. 7A-7N and 7P are serial views illustrating an embodiment of astep-by-step process for fabricating a suspension assembly and a circuitassembly according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

An embodiment of a suspension assembly 10 is illustrated in FIGS. 1-3.The suspension assembly 10 includes a load beam portion 12 having afirst end 12 a and a second end 12 b. A gimbal portion 14 is attached tothe first end 12 a of the load beam portion 12. The gimbal portion 14has a head assembly 16 mounted thereon.

A plurality of traces 18 are attached to the load beam portion 12. Thetraces 18 extend between the first end 12 a and the second end 12 b ofthe load beam portion 12. A first end 18 a, FIG. 2, of each one of thetraces 18 is electrically connected to corresponding terminals (notshown) of the head assembly 16. A second end 18 b, FIGS. 1 and 4B, ofeach one of the traces 18 extends from the second end 12 b of the loadbeam portion 12. Each one of the traces 18 includes a corresponding lead22 for being electrically connected to a related component of a harddisk drive.

A portion of each one of the traces 18 is covered with a protectivelayer 20, FIGS. 1, 2, 4A and 4B, such as a non-conductive photoimageablecovercoat material. Examples of suitable photoimageable covercoatmaterials include epoxy acrylate formulations offered by Taiyo under thePSR4000 series and by Nippon Polytech under the NPR80 series; andpolyimide formulations offered by Arch Chemicals under the Probimideseries and by DuPont under the Pyralin Series. An example of a suitablescreen printable covercoat material for the protective layer 20 includesan epoxy formulation offered by Ashai Chemicals under the part numberCCR232. The protective layer 20 reduces the potential for corrosion ofthe underlying portions of the traces 18. As is commonly practiced inart of circuit-making, the portions of the traces 18 that are notcovered by the protective layer 20 typically have a coverplate layer(not shown) of corrosion-resistant material such as gold or palladiumformed thereon.

Referring to FIG. 4A, the load beam portion 12 includes a base member24. The traces 18 are mounted directly on a first side of the basemember 24. The traces 18 as well as other types of conductive featuresare formed from a conductive feature layer formed on the base member 24.A reference voltage member 26 is mounted directly on a second side ofthe base member 24. The traces 18 and the reference voltage member 26are preferably mounted directly on the respective first and second sidesof the base member 24. By being mounted directly on a surface, it ismeant that an attachment layer such as a layer of adhesive is not usedbetween the base member 24 and the traces 18 or the reference voltagemember 26. A support member 28 is mounted on a surface of the referencevoltage member 26 opposite the second side of the base member 24. Thesupport member 28 includes a main portion 28 a having spaced apartflange members 28 b extending therefrom. The flange members have athickness 28 b′ that is substantially greater than a thickness 28 a′ ofthe main portion 28 a.

The base member 24 is typically a flexible polymeric substrate having athickness of from about 0.25 mils to about 3.0 mils. The specificapplication and design of the suspension assembly 10 will dictate therequired thickness of the base member 24. Suitable materials for thebase member 24 include a polyimide film such as that sold by DuPontunder the tradename KAPTON® E. Other types of commercially availableflexible polymeric films, such as, for example, films made of polyesterand polypropylene, e.g., those available from DuPont Corporation underthe trade name Mylar®, may also be useful as materials for the basemember 24. In an alternative embodiment, the base member may be formedfrom a liquid crystal polymer (LCP), especially a multiaxially orientedliquid crystal polymer. Such polymers have been disclosed in U.S. Pat.No. 4,975,312, and are commercially available from Hoechst CelaneseCorporation under the trade name Vectra®, and from Amoco Corporationunder the trade name Xydar®. Properties of LCP films include electricalinsulation, moisture absorption of less that 0.5% at saturation, acoefficient of thermal expansion which is similar to that of the copperused for plated through holes, and a dielectric constant not to exceed3.5 over the functional frequency range of 1 kHz to 45 kHz.

The conductive traces 18 and the reference voltage member 26 arepreferably made of a conductive material such as copper. Preferredmaterials for the conductive traces 18 and the reference voltage member26 have a tensile strength of less than about 60,000 psi and aresistance of less than about 1.7 μΩ/cm at room temperature. Theconductive traces 18 and the reference voltage member 26 may include aplurality of layers of the conductive material. For example, a firstlayer of copper may be formed on the base member 24 using a depositionmethod, such as sputtering, and a second layer of copper may be formedon the first layer of copper using a plating process, such aselectroplating or electroless plating. Depending on the application, theoverall thickness of the conductive traces 18 and the reference voltagemember 26 is typically from about 50 micro inches to about 1000 microinches. The specific application and design of the suspension assembly10 will dictate the required thickness of the conductive traces 18 andthe reference voltage member 26.

The support member 28 is preferably made of a material having mechanicalproperties superior to the material of the traces 18 and referencevoltage member 26. The mechanical properties of the support member 28dominate the resulting overall stiffness of the load beam portion 12 ofthe suspension assembly 10. Depending on the stiffness and springproperties required in a given application, the typical thickness ofmain portion 28 a of the support member 28 is from about 0.1 mils toabout 1.5 mils. The support member 28 may include one or more flangedportions that are substantially thicker than the main portion thereof.

Preferred materials for the support member 28 include nickel-basedalloys, such as nickel-phosphorus alloys and nickel-boron alloys.Preferred nickel-based alloys have a tensile strength of greater thanabout 90,000 psi.

In most conventional suspension assemblies and circuit assemblies,stainless steel is the preferred material for the support member.However, stainless steel cannot be readily and reliably plated.Accordingly, support members 28 according to the present invention aremade of plateable materials such as nickel based alloys. In addition tobeing plateable, nickel-based alloys have material characteristics verysimilar to stainless steel.

In suspension assemblies and circuit assemblies according to the presentinvention, the configuration and construction of the reference voltagemember 26 relative to the traces 18 provide a highly controlledimpedance level. The material that the reference voltage member 26 ismade from has significantly higher electrical conductivity than that ofthe materials from which the support member 12 and conventional loadbeams are made. Furthermore, because the traces 18 and the referencevoltage member 26 are formed directly on the respective first and secondsurfaces of the base member 24, the distance between the referencevoltage member 26 and the traces 18 is more uniform when compared toprevious types of constructions. These structural features contribute toenhanced impedance performance.

As illustrated in FIG. 4B, the second end 18 b of the traces 18 thatextend from the second end 12 b of the load beam 12 are carried on thefirst side of the base member 24. The reference voltage member 26 iscarried on the second side of the base member 24. The protective layer20 is formed over the traces 18. It is desirable that the traces 18extending from the second end 12 b of the load beam 12 exhibit a minimaldegree of stiffness. Accordingly, the support member 28 does not extendpast the second end 12 b of the load beam 12.

Referring now to FIGS. 5 and 6, an embodiment of a circuit assembly 110according to the present invention is illustrated. The circuit assembly110 is made according to processes of the present invention. In use, thecircuit assembly 110 is mounted on a conventional load beam (not shown)for providing electrical interconnection between a head assembly 116 andthe associated electrical components of a hard disk drive (not shown).Additionally, the circuit assembly 110 includes a gimbal portion 114 forproviding the gimballing function. The circuit assembly 110 mayoptionally include a support member 128 for providing a suitable degreeof stiffness. An advantage of using the circuit assembly 110 inconjunction with a conventional load beam is that the thickness of thegimbal portion 114 can be significantly less than the thickness of agimbal portion of a conventional load beam. Accordingly, control of themovement of the head assembly 116 is improved.

The circuit assembly 110 includes a base member 124. A plurality oftraces 118 are formed directly on a first side of the base member 124and a reference voltage member 126 is formed directly on a second sideof the base member 124. A protective layer 120 is formed over the traces118. The support member 128 is formed directly on the reference voltagemember 126.

A process for making suspension assemblies and circuit assembliesaccording to the present invention is illustrated in FIGS. 7A-7N and 7P.A first side 200 a and a second side 200 b of a base substrate 200 aremetallized using a known deposition process, such as electroless,sputtering or chemical vapor deposition, with a first conductive layer202, commonly referred to as a seed layer, FIG. 7A. The base substrate200 is preferably a flexible polymeric film such as polyimide. In apreferred embodiment, the first conductive layer 202 has a thickness ofbetween about 200 angstroms and about 2000 angstroms and is made from ahighly conductive material such as copper.

The first conductive layer 202 provides a continuous conductive layer tofacilitate deposition of a second conductive 204, FIG. 7B. The secondconductive layer 204, commonly referred to as a flash plated layer, isalso made of a highly conductive material such as copper. The first andsecond conductive layers 202, 204 on the first side 200 a of the basesubstrate 200 jointly define a conductive feature base layer 207, FIG.7B. The first and second conductive layers 202, 204 on the second side200 b of the base substrate 200 jointly define a reference voltage layer209.

The second conductive layer 204 is deposited using a known platingprocess, including processes such as electroless plating orelectroplating techniques. A preferred method is electroplating and atypical plated thickness of the second conductive layer 204 is betweenabout 50 micro inches and about 1000 micro inches.

In instances where the second conductive layer is copper, copper iselectroplated from a copper sulfate & sulfuric acid plating solution.The plating current density is maintained between about 10 and about 60amps per square foot.

Following the formation of the conductive feature base layer 207 and thereference voltage layer 209, an etching process is performed thereon toprepare the surfaces thereof for application of a photoresist. Typicaletching solutions for copper include, but are not limited to, ammonium,sodium persulfate and hydrogen peroxide sulfuric.

A photoresist layer 206 is then applied to the conductive feature baselayer 207 and to the reference voltage layer 209, FIG. 7C. In apreferred embodiment, the photoresist layer 206 is an aqueousprocessible, dry-film, positive-acting photoresist applied using heatand pressure. The thickness of the photoresist 206 is typically betweenabout 15 micrometers and about 50 micrometers. Suitable photoresists forthe photoresist layer 206 include, for example, photoresists offered byMacDermid Incorporated under the series designations SF, CF, and MP.Specific examples include MacDermid SF310 and MP413 photoresists.

After lamination of the photoresist 206, suitable photomasks 208 areengaged against the photoresist layers 206 and the photoresist layers206 are then exposed to energy from a suitable source for exposing adesired image in the photoresist layer 206, FIG. 7D. An ultravioletlight source is commonly used for exposing images in photoimageablephotoresists, such as those photoresist materials identified above. Thephotomasks 208 include patterned chrome or emulsion coated portions forpreventing the transmission of energy to specific areas of thephotoresist layer 206, allowing energy to pass through and react withthe photoresist layer 206 in unblocked areas. Photomasks of variousconstructions are commercially available.

Following exposure of the photoresist layer 206, areas of thephotoresist layer 206 that are not exposed to energy can be developed ina suitable developing solution. In a preferred embodiment where anaqueous positive-acting photoresist layer 206 is used, the areas nothaving been exposed to energy from the light source are developed out(removed) during the developing step, resulting in a desired circuitpattern in the photoresist layer 206, FIG. 7E. In the case of aqueousprocessible photoresists, the developing step includes applying a diluteaqueous solution, such as a 0.5%-1.5% sodium or potassium carbonatesolution, to the photoresist until the desired patterns are obtained inthe layers of photoresist layers 206. The developing step is typicallyperformed using commercially available equipment and solutions.

Following the developing step, areas of the conductive feature baselayer 207 that are exposed through the photoresist layer 206 are readyfor plating, FIG. 7E. To prevent plating on the reference voltage layer209, a protective layer 210, is applied over the developed photoresistlayer 206 on the reference voltage layer 209. One example of a suitableprotective layer 210 is a polymeric sheet held in place by a layer ofcommercially available, releasable adhesive. The polymeric sheet andadhesive are selected from materials that are resistant to the platingchemistry. After the protective layer 210 has been applied, exposedportions of the conductive feature base layer 207 are plated, FIG. 7F,to produce a plurality of conductive features 211 such as traces,bonding pads, capture pads, test pads, etc. Suitable plating methodsinclude the same method used to plate the second conductive layer 204. Apreferred method for plating is electroplating and a preferred materialis copper. The thickness of the conductive features 211 is typicallybetween about 0.2 mils and about 2.0 mils.

Following plating of the conductive features 211, FIG. 7G, theprotective layer 210 is removed and a protective layer 213, such as apositive acting photoresist layer, is applied over the conductivefeatures 211.

Next, the reference voltage layer 209 is subjected to an etching processto remove any oxidation. Typical etching solutions for copper include,but are not limited to, ammonium, sodium persulfate and hydrogenperoxide sulfuric.

Following the etching process, FIG. 7H, a support member layer 220 isformed on the reference voltage layer 209. The support member layer 220is formed on the reference voltage layer 209 using a suitable platingprocess. A preferred plating process is an electroless, preferablyautocatalytic, plating process. Specific information relating toelectroless autocatalytic plating is provided in ASTM B374. Preferredplating materials include nickel-based alloys such as anickel-phosphorus alloy having a phosphorus content of from about 5% toabout 15% and a nickel-boron alloy having a boron content of from about0.3% to about 10%.

A typical electroless autocatalytic plating process includes exposingthe reference voltage layer 209 to a plating bath comprising anickel-phosphorus alloy solution maintained at a temperature of betweenabout 170 degrees F. and 200 degrees F. and having a pH level of betweenabout 4.2 and about 6.2. The nickel concentration is maintained between0.05 and 1 oz/gal of nickel concentration. The phosphorous is includewith a reducing agent and deposits in the plated metal at a rate of 5.0to 7.0 wgt %.

Following plating of the support member layer 220, FIG. 71, thephotoresist layers 206 and 213 are removed using the previouslymentioned photoresist stripping method. Then, the portions of theconductive feature base layer 207 and reference voltage layer 209 thatwere concealed under the corresponding photoresist layer are removedusing a suitable etching process, such as the etching processesdescribed above. By etching previously concealed portions of theconductive feature base layer 207 and reference voltage layer 209, theconductive features become electrically isolated from each other.

In order to achieve superior performance characteristics, a suspensionassembly or a circuit assembly may require additional torsional rigidityor apertures extending through the base substrate 200. FIGS. 7J-7Pillustrate suitable process steps for adding additional thickness toselected portion of the support member layer 220 and for formingapertures through the base substrate 200.

As illustrated in FIG. 7J, a photoresist layer 222 is formed over theconductive features 211 and the support member layer 220. In a preferredembodiment, the photoresist layer 222 is made from the same material asthe photoresist layer 206, described above in reference to FIG. 7C.Next, as illustrated in FIG. 7K, the photoresist layer 222 is exposedand developed using the same exposure and develop methods describedabove in reference to FIGS. 7D and 7E. The photoresist layer 222adjacent to the conductive features 211 is flood exposed such that itremains in its entirety after the developing step. The photoresist layer222 adjacent to the support member layer 220 is exposed through aphotomask 224 that includes energy blocking portions 224 a that arealigned with the support members 220. The energy blocking portions 224 aare configured such that after exposure and developing of thecorresponding photoresist layer 222, the remaining exposed portions ofthe photoresist layer 222 cover only a portion of the support memberlayer 220, FIG. 7L.

Next, as illustrated in FIG. 7M, the support member layer 220 issubjected to an additional plating process. The additional platingprocess produces raised portions 220 a formed on the previously platedportions of the support member layer 220. The plating process of FIG. 7Mis preferably the same plating process as described above in referenceto FIG. 7H. Following the plating process, FIG. 7N, the photoresistlayers 222 are removed.

Next, apertures 226 through the base substrate 200, FIG. 7N, are formedtherein using a variety of different methods. Suitable methods forforming include mechanical punching, laser ablation, laser drilling, andchemical milling. In a preferred embodiment, the base substrate 200 is apolyimide film and the apertures 226 are formed using a suitablechemical milling process. The chemical milling process includes exposingthe polyimide base substrate 200 to a concentrated base solution such aspotassium hydroxide (KOH) at a temperature of from about 50° C. to about120° C. In doing so, portions of the base substrate 200 exposed to thebase solution are etched, producing the apertures 226.

Lastly, as illustrated in FIG. 7P, a coverplate layer 228 is formed onthe conductive features 211 to provide enhanced performancecharacteristics such as corrosion resistance and bond strength. Suitablematerials for the coverplate layer 228 include gold, palladium, tin andnickel. Several methods are known in the art for depositing thecoverplate layer 228.

A hard disk drive suspension assembly according to the present inventionimproves control of the suspension stiffness in three ways. First, thethickness of a plated suspension is much less than current suspensions.Conventional suspensions having a stainless steel support member startto reach a minimum thickness limit at approximately 1 mil to about 0.5mil using current rolling and stamping techniques. Second, the thicknessof support members according to the present invention can be tailored toachieve a number of specific design requirements, such as by controllingthe dwell time of the assembly in the plating bath. Third, regionalstiffness of the support member can be tailored through the specificplating process.

Improved head fly characteristics are achieved through greater designfreedom in attaining precise regional stiffness and torsioncharacteristics. Conventional load beams are formed from a continuouspiece of stainless steel material. This type of construction does notpermit isolated islands or multiple material thickness. With a platedsuspension according to the present invention, the base member allowsthe support member to include islands. This additional designcharacteristic allows the overall and regional stiffness and torsionalcharacteristics of the suspension assemblies to be tailored. The abilityto precisely control the torsion and stiffness characteristics of asuspension assembly is essential. Such control allows the head torespond faster and in a more controlled manner to changes in the surfaceprofile of the disk. By improving this control, the head assembly can bepositioned closer to the disk without increasing the potential of thehead contacting the disk. By flying the head assembly closer to thedisk, the quantity of information stored on a disk can be increased.

Many conventional suspension assemblies include a separately fabricatedflexible circuit that is attached to a load beam using an adhesive suchas an epoxy. This type of fabrication technique is currently done byhand. Accordingly, it is labor intensive and susceptible to significantprocess variations. Suspension assemblies according to the presentinvention significantly reduce fabrication time and process variation.

Suspension assemblies and circuit assemblies according to the presentinvention also exhibit improved manufacturability. The reference voltagelayer and conductive feature layer increase the stability of the webduring processing, making the web easier to process. Furthermore,because the thickness of the support member can be reduced overconventional suspension assemblies, the thickness of the polymeric basesubstrate can be optimized for processing. Suspension assembliesaccording to the present invention have a construction that counteractscoefficient of thermal expansion (CTE) mismatches, reducingstress-induced curling.

As the data transmission rates in hard drives increase, suspensionassemblies and related circuit assemblies will need to provide highlycontrolled impedance characteristics. Current suspension assembliesprovide only limited impedance control due to significant variability inthe distance between the traces and reference voltage member. Insuspension assemblies that use a conventional stainless steel load beamas a reference voltage layer, impedance characteristics are alsoadversely affected by the poor conductivity of stainless steel. When aseparately fabricated flexible circuit is used in a suspension assemblyto electrically connect the head assembly to the related electroniccomponents, variations in the spacing between the flexible circuit andthe reference voltage member adversely affect impedance characteristics.

By forming the reference voltage layer and the traces directly on thebase substrate in the present invention, the spacing between the tracesand the reference voltage layer is precisely controlled. Also, inpreferred embodiments according to the present invention, the referencevoltage layer is made from a highly conductive material and the supportmember is made from a material providing essential mechanicalproperties. These design characteristics significantly improve theimpedance performance of suspension assemblies and circuit assembliesaccording to the present invention.

Accordingly, it is appropriate that the appended claims be construedbroadly and in a manner consistent with the scope of the embodiments anddescriptions disclosed herein.

By forming the reference voltage layer and the traces directly on thebase substrate in the present invention, the spacing between the tracesand the reference voltage layer is precisely controlled. Also, inpreferred embodiments according to the present invention, the referencevoltage layer is made from a highly conductive material and the supportmember is made from a material providing essential mechanicalproperties. These design characteristics significantly improve theimpedance performance of suspension assemblies and circuit assembliesaccording to the present invention.

Accordingly, it is appropriate that the appended claims be construedbroadly and in a manner consistent with the scope of the embodiments anddescriptions disclosed herein.

What is claimed is:
 1. A circuit assembly for a disk drive suspensionassembly, comprising: a polyimide base member; a plurality of tracesformed directly on a first surface of the base member, the tracesextending between a first end and a second end of the base member; areference voltage layer formed directly on a second surface of the basemember, the plurality of traces overlaying at least a portion of thereference voltage layer; a support member formed directly on at least aportion of the reference voltage layer, wherein the reference voltagelayer is formed from a first electrically conductive material and thesupport member is formed from a second electrically conductive material,and wherein the first electrically conductive material providessubstantially greater electrical conductivity and substantially lesstensile strength than the second electrically conductive material.
 2. Acircuit assembly for a disk drive suspension assembly, comprising: apolyester base member; a plurality of traces formed directly on a firstsurface of the base member, the traces extending between a first end anda second end of the base member; a reference voltage layer formeddirectly on a second surface of the base member, the plurality of tracesoverlaying at least a portion of the reference voltage layer; a supportmember formed directly on at least a portion of the reference voltagelayer, wherein the reference voltage layer is formed from a firstelectrically conductive material and the support member is formed from asecond electrically conductive material, and wherein the firstelectrically conductive material provides substantially greaterelectrical conductivity and substantially less tensile strength than thesecond electrically conductive material.
 3. A circuit assembly for adisk drive suspension assembly, comprising: a liquid crystal polymerbase member; a plurality of traces formed directly on a first surface ofthe base member, the traces extending between a first end and a secondend of the base member; a reference voltage layer formed directly on asecond surface of the base member, the plurality of traces overlaying atleast a portion of the reference voltage layer; a support member formeddirectly on at least a portion of the reference voltage layer, whereinthe reference voltage layer is formed from a first electricallyconductive material and the support member is formed from a secondelectrically conductive material, and wherein the first electricallyconductive material provides substantially greater electricalconductivity and substantially less tensile strength than the secondelectrically conductive material.
 4. A circuit assembly for a disk drivesuspension assembly, comprising: a polyimide base member; a plurality oftraces formed directly on a first surface of the base member, the tracesextending between a first end and a second end of the base member; areference voltage layer formed directly on a second surface of the basemember, the plurality of traces overlaying at least a portion of thereference voltage layer; and a support member formed directly on atleast a portion of the reference voltage layer, wherein the supportmember includes a first portion having a first thickness and a secondportion having a second thickness, the second thickness beingsubstantially greater than the first thickness.
 5. A circuit assemblyfor a disk drive suspension assembly, comprising: a polyester basemember; a plurality of traces formed directly on a first surface of thebase member, the traces extending between a first end and a second endof the base member; a reference voltage layer formed directly on asecond surface of the base member, the plurality of traces overlaying atleast a portion of the reference voltage layer; and a support memberformed directly on at least a portion of the reference voltage layer,wherein the support member includes a first portion having a firstthickness and a second portion having a second thickness, the secondthickness being substantially greater than the first thickness.
 6. Acircuit assembly for a disk drive suspension assembly, comprising: aliquid crystal polymer base member; a plurality of traces formeddirectly on a first surface of the base member, the traces extendingbetween a first end and a second end of the base member; a referencevoltage layer formed directly on a second surface of the base member,the plurality of traces overlaying at least a portion of the referencevoltage layer; and a support member formed directly on at least aportion of the reference voltage layer, wherein the support memberincludes a first portion having a first thickness and a second portionhaving a second thickness, the second thickness being substantiallygreater than the first thickness.
 7. A disk drive suspension assembly,comprising: a polyimide base member; a plurality of traces formeddirectly on a first surface of the base member, the traces extendingbetween a first end and a second end of the base member; a referencevoltage layer formed directly on a second surface of the base member,the reference voltage layer formed from a first electrically conductivematerial and the plurality of traces overlaying at least a portion ofthe reference voltage layer; and a support member formed directly on atleast a portion of the reference voltage layer, the support memberformed from a second electrically conductive material, the firstelectrically conductive material providing substantially greaterelectrical conductivity and substantially lower tensile strength thanthe second electrically conductive material, the support memberincluding a head gimbal portion having a first thickness and a flangeportion having a second thickness, the second thickness beingsubstantially greater than the first thickness.
 8. A disk drivesuspension assembly, comprising: a polyester base member; a plurality oftraces formed directly on a first surface of the base member, the tracesextending between a first end and a second end of the base member; areference voltage layer formed directly on a second surface of the basemember, the reference voltage layer formed from a first electricallyconductive material and the plurality of traces overlaying at least aportion of the reference voltage layer; and a support member formeddirectly on at least a portion of the reference voltage layer, thesupport member formed from a second electrically conductive material,the first electrically conductive material providing substantiallygreater electrical conductivity and substantially lower tensile strengththan the second electrically conductive material, the support memberincluding a head gimbal portion having a first thickness and a flangeportion having a second thickness, the second thickness beingsubstantially greater than the first thickness.
 9. A disk drivesuspension assembly, comprising: a liquid crystal polymer base member; aplurality of traces formed directly on a first surface of the basemember, the traces extending between a first end and a second end of thebase member; a reference voltage layer formed directly on a secondsurface of the base member, the reference voltage layer formed from afirst electrically conductive material and the plurality of tracesoverlaying at least a portion of the reference voltage layer; and asupport member formed directly on at least a portion of the referencevoltage layer, the support member formed from a second electricallyconductive material, the first electrically conductive materialproviding substantially greater electrical conductivity andsubstantially lower tensile strength than the second electricallyconductive material, the support member including a head gimbal portionhaving a first thickness and a flange portion having a second thickness,the second thickness being substantially greater than the firstthickness.